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Les vignerons du Val de Loire souhaitent faire évoluer les différents types de vins liquoreux produits actuellement dans leurs appellations en lien avec l’élaboration d’une qualité de raisin correspondant à ces types. Pour cela, il est nécessaire de caractériser objectivement les baies de raisin et leur qualité.Notre étude porte sur le développement d’une méthode multicritères combinant des mesures physiques et biochimiques des raisins, permettant d’identifier et de caractériser différents niveaux de développement de la pourriture noble sur raisins de Chenin blanc dans un objectif de production de vins liquoreux.Pour cela, des raisins correspondant à trois niveaux de pourriture noble ont été sélectionnés, lors de deux millésimes, 2012 et 2013. Des analyses classiques de qualité du raisin ont été réalisées et complétées par des analyses de couleur, de texture et de composés phénoliques.Outre la caractérisation phénolique du Chenin (sain et botrytisé), cette étude met en évidence la présence de myricétine, que l’on retrouve traditionnellement dans les variétés de raisin rouge, et qui semblerait être aussi synthétisée dans les baies de raisins blancs fortement atteintes par la pourriture noble.Nous avons également montré qu’une analyse multicritères permet une très bonne différenciation des baies plus ou moins botrytisées. Une combinaison des teneurs en myricétine, astilbine et glycérol permet notamment une très bonne discrimination des baies en fonction de leur niveau de botrytisation. Enfin, nous avons détectés de nouveaux composés dans les baies suite à l’attaque fongique, qui pourraient provenir de réactions d’oxydation. Ces résultats restent toutefois à confirmer. / Winemakers from the Loire valley are willing to improve the various types of sweet wines currently produced in their designation of origin altogether with the elaboration of grape quality that corresponds to these wines. For that purpose, it is necessary to objectively characterize the grapes and their quality. Our study implies the development of a multcriteria method that combines physical and biochemical measures on the grape, allowing the identification and characterization of the different levels of noble rot development on Chenin blanc grapes for the production of sweet wines. To do so, grapes corresponding to three noble rot levels were selected during two vintages, 2012 and 2013. Classical analysis of grape quality were carried out and complemented with color, texture and phenolic composition analysis. Besides the phenolic characterization of Chenin (healthy and botrytised), this study revealed the presence of myricetin, that is traditionally detected on red grape varieties, and that seems to be also synthetized on white grapes strongly affected by noble rot. We have also showed that a multicriteria analysis brings a very good differentiation of grapes more or less botrytised. A combination of myricetin, astilbin and glycerol concentrations showed a significantly good discrimination of grapes according to botrytisation level. Finally, we have detected new compounds on the grapes after the fungal attack that could be the result of oxidative reactions. These results are to be confirmed

Thesis (MSc)--Stellenbosch University, 2012 / ENGLISH ABSTRACT: The aroma and flavour of wine are important aspects that form the basis for consumers’ organoleptic experience of wine. Therefore, an understanding of the chemical composition of wine aroma is of major importance, to establish possible links between wine chemistry, sensory attributes and consumer preference for a product. For this purpose analytical chemistry and multivariate techniques are indispensable tools for the metabolic profiling of wine. Chenin blanc is one of the most important South African export white wine varieties. However, despite its importance, very limited profiling of Chenin blanc aroma compounds has been done and information is restricted to isolated and dated reports on a few chemical compounds only. Therefore, the overall aim of this study was to obtain an in-depth view of the volatile chemical profile of this cultivar. The first task was to perform targeted volatile metabolic profiling of the three dry and offdry Chenin blanc styles, fresh and fruity, rich and ripe unwooded and rich and ripe wooded. To this end, a new, simple and robust liquid-liquid extraction technique using dichloromethane was developed and validated for extraction of analytes prior to gas chromatography flame ionization detection (GC-FID) analysis, to quantify 57 analytes in one rapid analytical procedure. This method was applied to profile 48 Chenin blanc wines. Very successful discrimination between the three styles, using the quantified volatile compounds, was obtained with two multivariate methods. These were partial least squares regression-discriminant analysis, (PLS-DA), as well linear-DA, using best subset selection for identifying the most important variables. According to the classification models, a higher content of maturation derived, malolactic fermentation derived and wood derived compounds were predominantly characteristic of the wooded wines. Higher content of some terpenes and ethyl esters were predominantly associated with the rich and ripe unwooded style Chenin blanc wines, while the fresh and fruity style were generally characterized by high levels of acetate esters. Secondly, untargeted analysis of 21 wines was done with gas chromatography mass spectrometry (GC-MS). Mathematical chromatography, using PARAllel FACtor analysis (PARAFAC and PARAFAC2), was applied to the GC-MS data for resolution of the complex chromatographic results by multi-way modeling, and to derive unbiased multivariate classification models of the three styles. This approach provided excellent style differentiation, without the arduous task of analysis of numerous standards and setting up of calibration curves, required by the targeted approach described above. Additionally, the data generated during this study will form part of the current South African wine aroma database, which does not contain any data regarding Chenin blanc at present. / AFRIKAANSE OPSOMMING: Die aroma en geur van wyn is belangrike aspekte aangesien dit die basis vorm van die wynverbruiker se organoleptiese ervaring van die produk. Derhalwe, is ‘n deeglike kennis van die chemiese samestelling van wynaroma baie belangrik, ten einde die korrelasies tussen wynchemie, sensoriese eienskappe en verbruikersvoorkeure te bepaal. Vir hierdie doel, is die insameling van analitiese chemiese data, tesame met multi-veranderlike tegnieke om relevante inligting uit die data te onttrek, onmisbaar vir die metaboliese profilering van wyn. Chenin blanc is huidiglik een van Suid-Afrika se belangrikste uitvoer wit wynvariëteite. Ten spyte hiervan, is daar tot hede egter baie min profilering van Chenin blanc se aromakomponente gedoen en die beskikbare inligting is beperk tot geïsoleerde en verouderde navorsingsbevindinge. In die lig van bogenoemde, is die oorkoepelende motivering vir hierdie studie dus om die vlugtige chemiese komponente se profiel in Chenin blanc wyn, in diepte te bepaal. Die eerste taak was die geteikende bepaling van die metaboliese profiel van drie droë of halfdroë Chenin blanc wynstyle, nl. vars en vrugtig, ryk en ryp ongehout, asook ryk en ryp gehout. Om dit te bereik, is ‘n nuwe eenvoudige en robuuste vloeistof-vloeistof ekstraksieprosedure met dichlorometaan ontwikkel, wat analise met gaschromatografie – vlamionisasie deteksie (GC-FID) voorafgaan, om die konsentrasies van 57 komponente in een vinnige analise te bepaal. Hierdie metode is gebruik om 48 Chenin blanc wyne te profileer. Deur gebruik te maak van multi-veranderlike data analitiese tegnieke, is die gekwantifiseerde vlugtige komponente data gebruik in diskriminant analise. Baie suksesvolle onderskeid tussen die drie style, is verkry deur gebruik te maak van twee multi-veranderlike metodes, naamlik: parsiële kleinste kwadrate regressie, diskriminant analise, asook liniêre diskriminant analise. Vir laasgenoemde analise, is die seleksie van die mees belangrike veranderlikes met beste sub-groep regressie bepaal. Volgens hierdie klassifikasie modelle is ‘n hoër inhoud van veroudering-, appelmelksuurgisting- en houtverwante aroma komponente baie kenmerkend in die houtbehandelde wyne. Hoër vlakke van sommige terpene en etiel esters was kenmerkend met betrekking tot ryk en ryp ongehoute Chenin blanc style, terwyl die vars en vrugtige style meer gekenmerk was met hoë vlakke van asetaat esters. Tweedens is ‘n seleksie van 21 wyne geanaliseer deur gebruik te maak van gaschromatografie – massa spektrometrie (GC-MS) in ‘n ongeteikende metaboliese profileringsbenadering. Wiskundige chromatografiese metodes, spesifiek, parallelle faktor analise (PARAllel FACtor analysis (PARAFAC and PARAFAC2)), was voorts gebruik om komplekse chromatogramme te prosesseer met wiskundige, multi-vlak modellering. Met hierdie nie-selektiewe benadering, is ook suksesvolle klassifikasiemodelle gegenereer vir die diskriminasie tussen die drie verskillende Chenin blanc style. Die voordeel van die ongeteikende GC-MS analise, gekoppel met die data hanterings- en prosesseringsprotokols in hierdie studie gebruik, is dat die arbeidsintensiewe taak om kalibrasiekurwes op te stel vir elke individuele komponent, soos wat vereis word in die geteikende benadering, nie nodig is nie. Die data wat ingewin is gedurende hierdie studie, sal ook bygevoeg word tot ‘n bestaande Suid-Afrikaanse aroma databasis, wat tans geen data aangaande Chenin blanc wyn bevat nie.

Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Producers of South African (SA) dry and semi-dry Chenin blanc table wines are currently experimenting with winemaking techniques to modulate the flavours of the predominantly fruity styles of this genre. An important stage during wine style development is sensory profiling paired with consumer acceptance testing, before wine is produced on industrial scale. With those aforementioned goals in mind, this study was conducted in partnership with two commercial SA wine cellars. The main focus of the study was an investigation into the treatment effects of two winemaking techniques, respectively grape skin contact and natural fermentation, on the sensory profiles of experimentally produced Chenin blanc wines. Results obtained with descriptive sensory analysis (DA) of the wines were compared to those obtained by two rapid sensory profiling methods, namely projective mapping (PM) and frequency of attribute citation (FC). A consumer preference study was also done on the wines. In order to understand the treatment effects better, the dominant non-Saccharomyces yeasts that were present during the natural fermentations were identified using polymerase chain reaction (PCR), while the major volatile chemical compounds were identified with chromatography and mass spectrometry. The sensory and chemical profiles of the naturally fermented wines were significantly different from those of the inoculated wines. PCR analysis identified some of the yeasts present during alcoholic fermentation. In comparison to the inoculated fermented wines, the naturally fermented wines were generally perceived to have more intense and riper tropical fruity aromas, with enhanced sweetness and reduced intensities of sourness, bitterness and astringency. The wines fermented on the skins (FoS) had lower ester and volatile thiol concentrations than the control wines (with no skin contact) and limited skin contact wines. Sensory attributes linked to the FoS wines included aromas of dried fruit, dried grass and a vegetative character, with an increased sour and bitter taste and astringent mouthfeel. In contrast, the wines that were produced with limited skin contact (12 hours) retained their tropical fruity aromas better than the FoS wines. Limited skin contact seemed to have had a less harsh effect on the taste and mouthfeel than the FoS wines. A consumer study was done to establish a Generation Y consumer group’s (18-35 years) preference for the different treated wines. Overall, the naturally fermented wines, which were described as having a strong tropical fruit character, were preferred. The FoS wines were generally disliked by the consumers. Results obtained from the three sensory analysis methods, respectively DA, PM and FC, were similar, thereby confirming the suitability of the rapid methods PM and FC, to extract qualitative information from the sensory profiling of white wine. The results of this study made a significant contribution towards validation of rapid sensory methods for wine evaluation, which are particularly valuable in the context of sustainability and technology transfer to research and industry alike. The knowledge gained on the chemical profiles of SA Chenin blanc is novel and this is one of the first reports on the volatile thiol content of SA Chenin blanc wine. / AFRIKAANSE OPSOMMING: Produsente van Suid-Afrikaanse (SA) droë en semi-droë Chenin blanc tafelwyne eksperimenteer tans met wynmaaktegnieke om die oorwegend vrugtige style van hierdie genre te varieer. ‘n Belangrike fase van wynstylontwikkeling is sensoriese profilering van die produkte met gepaardgaande verbruikersaanvaardingstoetse, voordat die wyne op industriële skaal geproduseer word. Met dié bogenoemde doelwitte in gedagte, was hierdie studie in vennootskap met twee kommersiële SA wynkelders gedoen. Die hooffokus van die studie was om die invloed van twee wynmaaktegnieke, onderskeidelik druifdopkontak en natuurlike fermentasie, op die sensoriese profiele van eksperimenteel geproduseerde Chenin blanc wyne te ondersoek. Resultate wat met beskrywende sensoriese analise (DA) van die wyne verkry is, is vergelyk met dié wat deur twee vinniger sensoriese profileringsmetodes metodes, naamlik projektiewe kartering (PM) en frekwensie van kenmerkaanhaling (FC) verkry is. 'n Verbruikervoorkeurstudie is ook op die wyne gedoen. Ten einde die behandelingseffekte beter te verstaan, is die dominante nie-Saccharomyces giste wat teenwoordig was tydens die natuurlike fermentasie geïdentifiseer met behulp van die polimerasekettingreaksie (PCR), terwyl die vernaamste vlugtige chemiese verbindings geïdentifiseer is met chromatografie en massaspektrometrie. Die sensoriese en chemiese profiele van die natuurlike gefermenteerde wyne was beduidend anders as dié van die geiinokuleerde wyne. PCR analise het sommige giste wat teenwoordig was tydens alkoholies fermentasie geïdentifiseer. In vergelyking met die geiinokuleerde wyne, het die natuurlik gefermenteerde wyne intenser en ryper tropiese vrugtige aromas getoon, met ‘n verhoogde perspesie van soetheid en laer intensiteite van suurheid, bitterheid en vrankheid. Die wyne wat berei is deur fermentasie op die druifdoppe (FoS) het laer konsentrasies van esters en vlugtige swawelverbinding gehad, as die kontrole wyne (geen dopkontak) en beperkte dopkontak wyne. Sensoriese eienskappe gekoppel aan die FoS wyne was geasssosieer met gedroogde vrugte, gedroogde gras en 'n vegetatiewe aroma, met gepaardgaande verhoogde suur en bitter smaakpersepsies en ‘n frank mondgevoel. In teenstelling, het die wyne wat geproduseer is met 'n beperkte dopkontak (12 uur) hul tropiese vrugtige aroma beter behou as die FoS wyne. Beperkte dopkontak het ook ‘n minder negatiewe uitwerking op die smaakpersepies van bitterheid en vrankheid gehad. ‘n Verbruikerstudie is gedoen om 'n groep jong Generasie Y verbruikers (18-35 jaar) se voorkeure vir die verskillende behandelings te bepaal. Oor die algemeen is die natuurlike gefermenteerde wyne, wat beskryf is met 'n sterk tropiese vrugtekarakter verkies, terwyl die groep nie van die FoS wyne gehou het nie. Resultate wat verkry is met drie sensoriese analise metodes, onderskeidelik DA, PM en FC, was soortgelyk en die geskiktheid van die vinniger metodes, PM en FC, om kwalitatiewe inligting van witwyn se sensoriese eienskappe te verkry, is bevestig. Die resultate verkry met hierdie studie maak ‘n beduidende bydrae tot die validering van vinniger sensoriese metodes vir wynevaluering, wat veral waardevol is in die konteks van volhoubaarheid en tegnologieoordrag na navorsing en die industrie. Die nuwe kennis wat in hierdie studie gegenereer is met die chemiese profilering van SA Chenin blanc wyn is baie waardevol en hierdie is een van die eerste narvorsingsprojekte oor die inhoud van vlugtige swawelverbings in SA Chenin blanc wyn.

Thesis (MSc)--Stellenbosch University, 2011 / ENGLISH ABSTRACT: South African Chenin blanc wine is characterised by its style diversity and has been receiving more industry limelight over the past few years. Three dry Chenin blanc wine styles are currently described by the wine industry as Fresh and Fruity (FF), Rich and Ripe unwooded (RR-unwooded) and, Rich and Ripe wooded (RR-wooded). According to the South African wine industry, however, consumers seem to be somewhat confused by these various Chenin blanc wine styles, which have not yet been clearly defined and classified. During this study we investigated the following perspectives of this wine style classification confusion: Currently, no specified sensory method is being used to differentiate between wine styles of a single wine cultivar, such as Chenin blanc. The sorting method can be used as a more cost and time effective classification and profiling method than general quantitative descriptive analysis (QDA). It was therefore investigated whether both uninstructed and instructed sorting, with consumers and wine experts, can be used to classify and describe the Chenin blanc wine styles similarly to QDA. The increase in young wine consumers, Generation Y, introduces new wine marketing opportunities for the wine industry which need to be investigated. Young consumers are not aware of the various Chenin blanc wine styles, which may influence their wine preferences. The influence of wine style knowledge on these consumers’ wine style preferences were investigated during blind and wine style informed preference test. Any segmentation within this Generation Y group was also investigated with regards to their Chenin blanc wine style preferences and/or exploratory data. The following scientific and industrial findings were made: QDA was successfully substituted by instructed and uninstructed sorting tasks. Although the sorting tasks easily differentiated between wooded and unwooded wines, QDA differentiated more successfully between the unwooded wines. Wine tasting experience did not significantly influence the sorting results of the consumers versus the wine experts, but more experienced panellists consistently used fewer descriptors than untrained consumers. All panellists sorted products slightly better when they were provided with wine style sorting instructions. However, there were no significant differences between the instructed and uninstructed sorting task results, i.e. a wine style descriptor list did not improve panellists’ abilities to describe their sorted wine groups. South African Chenin blanc wines can definitely be divided into wooded and unwooded wine styles, i.e. two wine style groups, but the unwooded Chenin blanc wine spectrum formed a wine-style-continuum. This finding is apparent from both the sorting and QDA methods. The unwooded continuum wines can further be differentiated from one another with the use of a fresh-to-mature scale and/or a light-to-full body scale during QDA. Generation Y wine consumers preferred all the Chenin blanc wine styles equally and moderately during the blind tasting, but their knowledge of the wine style concepts significantly increased their preferences for the wines during the informed wine style tasting. The cognitive influence of wine style knowledge is therefore powerful in terms of influencing a consumer’s wine preferences. Other interesting correlations were also made between Generation Y consumers’ wine style preferences and their exploratory data. / AFRIKAANSE OPSOMMING: Suid-Afrikaanse Chenin blanc wyn word gekarakteriseer deur styl diversiteit en is die afgelope paar jaar meer in die kollig. Drie droë Chenin blanc wynstyle word tans deur die wynbedryf beskryf as: Vars en Vrugtig, Ryk en Ryp ongehout en, Ryk en Ryp gehout. Volgens die Suid- Afrikaanse wynbedryf is daar heelwat verwarring is tussen hierdie Chenin blanc wynstyle weens die feit dat hierdie wynstyle nog nie duidelik gedefinieer en geklassifiseer is nie. Tydens die huidige studie het ons die volgende perspektiewe van hierdie wynstyl-verwarring ondersoek: Huidiglik word daar geen gespesifiseerde sensoriese metode gebruik om te onderskei tussen verskillende wynstyle van ’n enkele wyn kultivar, soos Chenin blanc, nie. Die sorteringsmetode kan gebruik word, instede van kwantitatiewe beskrywende analise, as ’n meer koste- en tyd-effektiewe produk klassifikasie en profileringsmetode. DIt was dus ondersoek of beide geïnstrukteerde en ongeïnstrukteerde sorteringstake, met verbruikers en wynkundiges, gebruik kan word om die verskeie Chenin blanc wynstyle kan profileer en klassifiseer soortgelyk soos kwantitatiewe beskrywende analise. Die toename in jong verbruikers, Generasie Y, skep nuwe wynbemarkingsgeleenthede wat ondersoek moet word. Jong verbruikers se onbewustheid van die verskeidenheid Chenin blanc wynstyle mag hulle voorkeure vir hierdie wyne beïnvloed. Die invloed van wynstyl kennis op hierdie jong verbruikers se wynstyl voorkeure was ook ondersoek gedurende ’n blinde en ’n wynstyl-ingeligte voorkeur toets. Enige segmentasie binne hierdie Generasie Y verbruikersgroep was ook ondersoek in verband met hul Chenin blanc wynstyl voorkeure en/of verkennende data. Die volgende wetenskaplike en industriële bevindings is gemaak: Kwantitatiewe beskrywende analise kan suksesvol vervang word deur beide geïnstrukteerde en ongeïnstrukteerde sorteringsmetodes. Alhoewel die sorteringsmetodes maklik gebruik kon word om te onderskei tussen gehoute en ongehoute wyne, kan kwantitatiewe beskrywende analise fyner onderskeid tref tussen die individuele ongehoute wyne. Die wynproe-ervaringsvlak het geen invloed op die sorteringsresultate gehad nie, maar meer ervare paneellede het konsekwent gebruik gemaak van minder beskrywende terme as onopgeleide verbruikers wat baie meer en verskillende soorte terme gebruik het. Beide panele het effens beter gesorteer wanneer hulle spesifieke wynstyl sorteringsinstruksies ontvang het. Daar was egter geen beduidende verskille tussen die geïnstrukteerde en ongeïnstrukteerde sorteringsresultate nie, wat daarop dui dat sorteringsinstruksies en ’n lys van wynstyl beskrywings nie die paneellede se wyse van sortering verander het nie. Suid-Afrikaanse Chenin blanc wyne kan definitief verdeel word in gehoute en ongehoute wynstyle, d.w.s twee wynstyl groepe, maar die ongehoute Chenin blanc wyn spektrum vorm ’n wynstyl-kontinuum. Laasgenoemde is bevind tydens beide die sorteringstake asook kwantitatiewe beskrywende analise. Die ongehoute kontinuum wyne kan verder van mekaar onderskei word met behulp van ‘n vars-tot-volryp en/of ‘n ligte-tot-volmond skaal tydens kwantitatiewe beskrywende analise. Alle jong wyn verbruikers het ewe veel van al die wynstyle gehou tydens die blinde wynstyl voorkeur toets, maar tydens die wynstyl-ingeligte voorkeur toets het hulle voorkeure vir al die wynstyle drasties verbeter. Die kognitiewe invloed van Chenin blanc wynstyl kennis kan dus lei tot hoër voorkeure vir die wynstyle. Ander interessante korrelasies is ook bevind tussen hierdie Generasie Y wyn verbruikersgroep se wynstyl voorkeure en hul verkennende data.